1. Field of the Invention
The invention relates to an improved tension indicating gage washer.
2. Description of the Prior Art
For some time now helical springs or lock washers have been used to measure the tension on a bolt. This is particularly true of the mining field where the tension on in situ mine roof bolts is to be determined. According to a recent report from the Rock Action Committee of the American Mining Congress, friction between the tightened washer and the bearing parts of the rock bolt has usually required about 40 percent of the installed tension to be released before the deformable washer shows an indication of opening. It is extremely dangerous to release this high percentile of tension when the bolt is supporting an overburden in a mine, especially in old mine workings that are being reopened for further use.
Split ring washers with indicator arms used as load gages are known as shown in U.S. Pat. Nos. 3,060,731 to H. H. Adise, and 3,534,651 to J. G. Belfiglio. With many of these types of washers the washer is either permanently deformed by the forces acting on it or it requires the releasing of a large amount of the bolt holding tension before an accurate indication of the load can be obtained. In my invention a simple, inexpensive, split ring washer is used as a load gage which can indicate a 10% change in tension without being permanently deformed or requiring the release of a large amount of initial tension.